Photonic device and fabrication method thereof

ABSTRACT

A method for fabricating a photonic device is provided. The method includes forming an optical coupler and a waveguide structure connected to the optical coupler over a semiconductor substrate; forming a metal-dielectric stack over the optical coupler and the waveguide structure; etching a hole in the metal-dielectric stack and vertically overlapping the optical coupler; and forming a protection layer on a sidewall and a bottom of the hole.

BACKGROUND

In today's telecommunication network, optical fibers are typicallychosen over electrical cablings to transmit information in the form oflight from one place to another partially because of variousadvantageous characteristics of the optical fibers, for example, ahigher bandwidth, a longer transmission distance, etc., when compared tothe electrical cablings.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic top view of a photonic device according to someembodiments of the present disclosure.

FIGS. 2A-2E illustrate a method for fabricating a photonic device atvarious intermediate stages of manufacture according to some embodimentsof the present disclosure.

FIGS. 3A-3B illustrate a method for fabricating a photonic device atvarious intermediate stages of manufacture according to some embodimentsof the present disclosure.

FIGS. 4A-4D illustrate a method for fabricating a photonic device atvarious intermediate stages of manufacture according to some embodimentsof the present disclosure.

FIG. 5 is a cross-sectional view of a photonic device according to someembodiments of the present disclosure.

FIG. 6 is a cross-sectional view of a photonic device according to someembodiments of the present disclosure.

FIG. 7 is a cross-sectional view of a photonic device according to someembodiments of the present disclosure.

FIG. 8 is a cross-sectional view of a photonic device according to someembodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Optical communication is a technique by which data signals can betransmitted from a transmitter to a receiver using optical fiber. Anoptical transmitter converts an electrical signal into an opticalsignal, which forms a carrier wave. The carrier wave is modulated with amodulation signal (i.e. the data), and is then transmitted along theoptical fiber to a receiver, which converts the optical signal back intoan electrical signal and recovers the transmitted data.

A photonic device and the methods of forming the same are provided inaccordance with some embodiments of the present disclosure. Theintermediate stages of manufacturing the photonic device areillustrated. Variations of the embodiments are also discussed.Throughout the various views and illustrative embodiments, likereference numbers are used to designate like elements.

FIG. 1 is a schematic top view of a photonic device 100 according tosome embodiments of the present disclosure. The photonic device 100 maybe a fiber-optical transceiver including a transmitter path 200 and areceiver path 300. It should be noted that, the transmitter path 200 andthe receiver path 300 in FIG. 1 are shown in a simplified manner.Additional components, such as amplifier or switches, may be present inthe transmitter path 200 and the receiver path 300 or between thetransmitter path 200 and the receiver path 300.

In some embodiments, the transmitter path 200 includes an optical source210, an optical coupler GC0, a modulator 220, an optical coupler GC1,and waveguides WG. The optical source 210 may be configured to providean unmodulated light. For example, the optical source 210 may be a laseror other source. In the present embodiments, the optical coupler GC0receives the unmodulated light from the optical source 210 and directsthe unmodulated light into the waveguides WG, thereby sending theunmodulated light toward the modulator 220. The modulator 220 isoptically coupled between the optical coupler GC0 and the opticalcoupler GC1 through the waveguides WG for adjusting the unmodulatedlight. For example, the modulator 220 is configured to modulate andadjust characteristics (e.g., modes) of the unmodulated light with amodulation signal (i.e. the data). After the modulation, anotherwaveguide WG sends the modulated light toward the optical coupler GC1,thereby outputting the modulated light from the optical coupler GC1, forexample, to an external fiber EF1. Additional component may be opticallycoupled between the optical coupler GC0 and the optical coupler GC1through waveguides WG.

The receiver path 300 may include a photodetector 310, an opticalcoupler CG2, and waveguides WG. In the present embodiments, thephotodetector 310 is optically coupled to the optical coupler GC2through the waveguides WG. Through the configuration, the opticalcoupler GC2 may receive a light signal (e.g., from an external fiberEF2), and directs the light signal into the waveguides WG, therebysending the light signal toward the photodetector 310. The photodetector310 may convert light signals into electrical signals, which can then beamplified and processed. Additional components may be optically coupledbetween the optical coupler GC2 and the photodetector 310 throughwaveguides WG.

In some embodiments, the photodetector 310, the optical couplersGC0-GC2, and the waveguides WG may be fabricated over a semiconductorsubstrate and covered by one or more layers (e.g., multi-levelinterconnect structure fabricated in a back-end-of-line (BEOL) process),and plural optical coupler openings O2 are respectively formed in thelayers above the optical couplers GC0-GC2 for optical coupling. Forexample, in some embodiments, light emitted from the optical source 210is sent to the optical coupler GC0 through the opening O2. In someembodiments, light may exit from the optical coupler GC1 and then besent to the external fiber EF1 through the opening O2. In someembodiments, light coming from the external fiber EF2 may be sent to theoptical coupler GC2 through the opening O2. The optical coupler openingsO2 are shown as dashed circles herein for brief illustration. In thecontext, the optical coupler openings O2 may also be referred to asoptical coupler holes.

In the present embodiments, the transmitter path 200 and the receiverpath 300 in combination form a fiber-optical transceiver on a chip. Insome other embodiments, the transmitter path 200 may form afiber-optical transmitter on one chip, while the receiver path 300 mayform a fiber-optical receiver on another chip. The fabricating processof the photodetector 310, at least one of the optical couplers GC0-GC2,and the waveguides WG is exemplarily illustrated below.

FIGS. 2A-2E illustrate a method for fabricating a photonic device (e.g.,the photonic device 100 in FIG. 1) at various intermediate stages ofmanufacture according to various embodiments of the present disclosure.For simplicity, some components of the photonic device are illustrated,while other components are omitted. The illustration is merely exemplaryand is not intended to be limiting beyond what is specifically recitedin the claims that follow. It is understood that additional operationsmay be provided before, during, and after the operations shown by FIGS.2A-2E, and some of the operations described below can be replaced oreliminated for additional embodiments of the method. The order of theoperations/processes may be interchangeable.

Reference is made to FIG. 2A. A semiconductor substrate 410 is provided,and a photodetector 310, a waveguide WG, and an optical coupler CG(e.g., any one of the optical couplers CG0-CG3 shown in FIG. 1) areformed over the semiconductor substrate 410. The semiconductor substrate410 may be a silicon-on-insulator (SOI) substrate including a basesubstrate 412, an insulator layer 414 over the base substrate 412, and asemiconductor layer 416 over the insulator layer 414. The base substrate412 may be a bulk substrate, such as bulk silicon substrate. Theinsulator layer 414 may include silicon oxide or other suitableinsulating materials, and/or combinations thereof. In some embodiments,an insulator layer 414 may include a buried oxide layer (BOX) that isgrown or deposited overlying the silicon base substrate 412. Thesemiconductor layer 416 may include an elementary semiconductor, such assilicon (Si) or germanium (Ge) in a crystalline structure; a compoundsemiconductor, such as silicon germanium (SiGe), silicon carbide (SiC),gallium arsenic (GaAs), gallium phosphide (GaP), indium phosphide (InP),indium arsenide (InAs), and/or indium antimonide (InSb); or combinationsthereof. For example, the SOI substrates are fabricated using separationby implantation of oxygen (SIMOX), wafer bonding, and/or other suitablemethods.

In some embodiments, the photodetector 310 includes a structure 416Apatterned from the semiconductor layer 416 and an epitaxialsemiconductor feature 420 over the structure 416A. The structure 416Amay be doped to have a first doped region 416AN and a second dopedregion 416AP, in which the first doped region 416AN has a firstconductive type (e.g., n-type) opposite to a second conductive type(e.g., p-type) of the second doped region 416AP. For example, the n-typedopants may include phosphorous, arsenic, antimony, or the like. Forexample, the p-type dopants may include boron, gallium, indium, or thelike. In some embodiments, the first doped region 416AN may have ann-type doping concentration higher than about 10¹⁸/cm³, and the seconddoped region 416AO may have a p-type doping concentration higher thanabout 10¹⁸/cm³.

An intrinsic semiconductor feature 420 is epitaxially grown in a recessof the structure 416A. In the present embodiments, the intrinsicsemiconductor feature 420 may include suitable pure semiconductormaterials, such as germanium (Ge), or the like in some embodiments. Forexample, germanium has a cut-off wavelength near ˜1.8 micrometers, andtherefore may be a promising candidate for photo-detection in the fieldof optical communication. In some alternative embodiments, the intrinsicsemiconductor feature 420 may include suitable semiconductor alloymaterials, such as silicon germanium (SiGe). In some other embodiments,rather than a Ge or SiGe epitaxial material being grown for theintrinsic semiconductor feature 420, other materials, such asmonocrystalline silicon, a binary semiconductor material (e.g., GaAs,InAs, InP, GaSb), tertiary semiconductor material (e.g., InGaAs), orother semiconductor material can be grown to form the intrinsicsemiconductor feature 420. The deposition process may be chemical vapordeposition (CVD) techniques (e.g., vapor-phase epitaxy (VPE) and/orultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/or othersuitable processes.

In some embodiments, the intrinsic semiconductor feature 420 is notintentionally doped, for example, not having intentionally diffuseddopants. However, the intrinsic semiconductor feature 420 may beunintentionally doped due to processes for fabricating elements otherthan the intrinsic semiconductor feature 420. For example, the intrinsicsemiconductor feature 420 is not intentional doped (NID) semiconductorlayers and thus free from the dopants in the doped regions 416AN and416AP. Alternatively, the intrinsic semiconductor feature 420 may bedoped with a p-type or an n-type with a doping concentration lower thanthat of the doped regions 416AN and 416AP. For example, the intrinsicsemiconductor feature 420 have dopant concentration lower than about10¹³/cm³.

The semiconductor feature 420 may have a material different from that ofthe underlying semiconductor structure 416A. For example, thesemiconductor feature 420 may include germanium (Ge), silicon germanium(SiGe), or other suitable semiconductor material, and the semiconductorstructure 416A may include silicon (Si). Through the configuration, thephotodetector 310 may be a semiconductor PIN waveguide photodiode thatexploits lateral Silicon/Germanium/Silicon (Si/Ge/Si) heterojunctions.Due to the refractive index difference between the semiconductor feature420 (e.g., Ge or SiGe) and the structures 416A (e.g., Si), incominglight coupled from the waveguide structure 416W (e.g., Si) into thesemiconductor feature 420 stays confined in the semiconductor feature420, and does not spread out in the doped regions 416AN and 416AP,avoiding any deleterious absorption of photo-generated carriers. In someother embodiments, the semiconductor feature 420 may have the samematerial as that of the underlying semiconductor structure 416A. Forexample, the semiconductor feature 420 may include silicon as theunderlying semiconductor structure 416A includes.

In some embodiments, the waveguide WG includes a waveguide structure416W patterned from the semiconductor layer 416. The waveguide structure416W has a higher refractive index than a refractive index of theinsulator layer 414, and therefore acts as the waveguiding core. In someembodiments, the optical coupler CG includes a coupler structure 416Cpatterned from the semiconductor layer 416. The coupler structure 416Cmay be a grating that has plural protruding portions 416CP spaced apartby the trenches CR. The protruding portion 416CP may have suitablewidths and pitches, such that the coupler structure 416C is capable ofdirecting the incident light with desired angle to the waveguidestructure 416W when receiving lights from a fiber or directing amodulated light from the waveguide structure 416W to a fiber. In someembodiments, the waveguide structure 416W connects the structure 416A tothe coupler structure 416C as illustrated in FIG. 1, such that thephotodetector 310 may receive the lights form the optical coupler CG.

A dielectric layer DL is formed surrounding and covering the structure416A, the coupler structure 416C, and the waveguide structures 416W. Insome embodiments, the dielectric layer DL may include an oxide (e.g.,SiO₂), an ultra-low k dielectric material, a low-k dielectric material(e.g., SiCO), SiON, or the like. In some embodiments, the dielectriclayer DL may be formed by a physical vapor deposition (PVD) process,chemical vapor deposition (CVD) process, flowable CVD process, atomiclayer deposition (ALD), or other suitable process, or the combinationthereof. In some embodiments, a refractive index of the material of thewaveguide structure 416W is higher than a refractive index of thematerial of the dielectric layer DL. Due to the difference in refractiveindices of the materials of the waveguide structure 416W and dielectriclayer DL, the waveguide structure 416W have high internal reflectionssuch that light is confined in the waveguide structure 416W, dependingon the wavelength of the light and the reflective indices of therespective materials. Through the configuration, the waveguide structure416W may have a strong optical confinement because it is surrounded bythe insulator layer 414 and a low-index material (e.g., the dielectriclayer DL).

A capping layer 230 may formed to cover a top surface of thesemiconductor feature 420 and the dielectric layer DL, therebyprotecting the semiconductor feature 420 from being exposed. The cappinglayer 230 may include suitable dielectric materials, such as siliconoxide, silicon nitride, silicon oxynitride, silicon nitrogen hydride(SiNH), the combination thereof, or the like.

A resist protection oxide (RPO) layer 250 is conformally formed over thecapping layer 230 and the dielectric layer DL. Then, an interlayerdielectric (ILD) layer ILD0 is formed over the RPO layer 250. In someembodiments, the ILD layer ILD0 may include an oxide (e.g., SiO₂), anultra-low k dielectric material, a low-k dielectric material (e.g.,SiCO), or the like. The ILD layer ILD0 may be an un-doped silicate glass(USG) or fluorosilicate glass (FSG) layer. In some embodiments, the ILDlayer ILD0 may be formed by a vapor deposition process. In someembodiments, prior to the formation of the ILD layer ILD0, an etch stoplayer 260 is conformally formed. The etch stop layer 260 may includesuitable material different from that of the ILD layer ILD0 and the RPOlayer 250. For example, in the present embodiments, the etch stop layer260 may include silicon nitride, silicon oxynitride, silicon carbide, orthe like.

Conductive contacts V0 are formed to connect the first doped region416AN and the second doped region 416AP. In some embodiments,implantation processes may be performed to the exposed portions of thefirst doped region 416AN and the second doped region 416AP, therebyforming highly doped contact regions HN and HP in the first doped region416AN and the second doped region 416AP, respectively. The highly dopedcontacts regions HN and HP in the first doped region 416AN and thesecond doped region 416AP may improve the ohmic contacts between theconductive contacts V0 and the semiconductor structure 416A. In someembodiments, the highly doped contact region HN has the first conductivetype (e.g., n-type). For example, the dopants implanted into the highlydoped contact region HN may be n-type dopants, such as phosphorous,arsenic, antimony, or the like. In some embodiments, the highly dopedcontact region HP has the second conductive type (e.g., p-type). Forexample, the dopants implanted into the highly doped contact region HPmay be p-type dopants, such as boron, gallium, indium, or the like. Theconductive contacts V0 may include one or more conductive materials. Insome embodiments, the one or more conductive materials may includetungsten (W), aluminum (Al), titanium (Ti), titanium nitride (TiN),and/or tantalum nitride (TaN). In some embodiments, a diffusion barrierlayer and/or a liner layer may be deposited into the contact openingsprior to depositing the one or more conductive materials.

A metal-dielectric stack (interchangeably referred to as multi-levelinterconnect structure) 270 is formed over the ILD layer ILD0, andconnecting the conductive contacts V0. The metal-dielectric stack 270includes plural ILD layers ILD1-ILD9 and a metallization pattern (e.g.,plural metal layers M1-M6 and plural metal vias V1-V5) embedded in theILD layers ILD1-ILD9. In some embodiments, the ILD layers ILD1-ILD9 mayinclude an oxide (e.g., SiO₂), an ultra-low k dielectric material, alow-k dielectric material (e.g., SiCO), or the like. The ILD layersILD1-ILD9 may include un-doped silicate glass (USG), hard black diamond(HBD), fluorosilicate glass (FSG), or the like. The metal layers M1-M6and the metal vias V1-V5 are in the ILD layers ILD1-ILD9, in which eachof the metal vias V1-V5 is connected between the two adjacent metallayers M1-M6. In some embodiments, the metal layers M1-M6 and the metalvias V1-V5 may include suitable metallic material such as aluminum,aluminum alloy, copper, copper alloy, titanium, titanium nitride,tantalum, tantalum nitride, tungsten, the like, and/or combinationsthereof. Formation of the metal-dielectric stack 270 may be adual-damascene process and/or a single-damascene process. Although theexemplary embodiments described herein depict six metal layers and fivemetal vias, this is merely illustrative and it should be understood thatthe photonic device may alternatively be formed with more or fewer metallayers and metal vias, depending on the application.

In some embodiments, etch stop layers ESL may be formed between adjacenttwo of the ILD layers ILD1-ILD9 for protecting the underlying materialfrom being etched when etching trenches or vias for the formation of themetal layers M1-M6 and the metal vias V1-V5. The etch stop layers ESLmay include suitable material other than that of the ILD layersILD1-ILD9. For example, the etch stop layers ESL may include siliconcarbide, silicon nitride, silicon oxynitride, the combination thereof,or the like. Oxide layers (e.g., tetraethoxysilane (TEOS) layers) OL maybe optionally formed over some of the etch stop layers ESL in someembodiments.

After the formation of the metal-dielectric stack 270, a passivationlayer 280 is formed over the ILD layer ILD9, and an opening O1 is thenetched in the passivation layer 280 and the ILD layer ILD9. A contactpad CP may be formed over the metal layer M6. The contact pad CP mayinclude suitable conductive materials, such as copper, aluminum, thecombination thereof, or the like. A conductive feature 300 may formed inthe opening O1 over the contact pad CP to connect the metal layer M6.The conductive feature 300 may include suitable conductive materials,such as aluminum. The conductive feature 300 may be a connector, such asconductive bumps, solder balls, etc. Through the conductive feature 300,electrical components (not shown), such as dies, may be electricallyconnected to the metal layer M6.

Reference is made to FIG. 2B. A patterned mask PM1 is formed over themetal-dielectric stack 270 and the passivation layer 280. The patternedmask PM1 has an opening PMO1 aligned with the coupler structure 416C.The patterned mask PM1 may include suitable organic material, such asphotoresist. For example, a photoresist is coated over themetal-dielectric stack 270 and the passivation layer 280 and thenpatterned using photolithography techniques to have the opening PMO1exposing portions of the passivation layer 280, thereby forming thepatterned mask PM1.

Reference is made to FIG. 2C. One or more etching processes areperformed to remove portions of the ILD layers ILD1-ILD9, the etch stoplayers ESL, and the oxide layers OL through the opening PMO1 of thepatterned mask PM1, thereby forming an opening O2 vertically overlappingthe coupler structure 416C in the metal-dielectric stack 290. Thepatterned mask PM1 may serve as an etch mask during the etching process.The etching process may include wet etch, dry etch, or the combinationthereof. For example, the etching process may include a dry etch usinggas etchants such as C₄F₈, CF₄, C₅F₈, Ar, O₂, the combination thereof,or the like. The etching process may be performed such that a topsurface of the ILD layer ILD1 is exposed. In the present embodiments,sidewalls of the ILD layer ILD1-ILD9, etch stop layers ESL, and theoxide layers OL may be exposed by the opening O2. The opening O2 may beused as a light path or waveguide to introduce light to the couplerstructure 416C. In some embodiments, the opening O2 has a rectangularcross-sectional profile with two parallel sidewalls perpendicular to atop surface of the semiconductor substrate 410. In some otherembodiments, the opening O2 has a tapered profile, in which a width at atop of the opening O2 is wider than a width at a bottom of the openingO2.

In some embodiments, the depth of the opening O2 may be designedaccording to product requirement, thereby improving coupling efficiency.For example, in the present embodiments, the etching process may becontrolled such that the opening O2 exposes a portion P12 of the ILDlayer ILD1, and the exposed portion P12 of the ILD layer ILD1 isrecessed and therefore thinner than other portions P11 of the ILD layerILD1. Through the configuration, a light source or a fiber may beoptically coupled to the coupler structure 416C through the recessedportion P12 of the ILD layer ILD1, the underlying etch stop layer ESL,the ILD layer ILD0, the layers 250, 260, and the dielectric layer DL.

Reference is made to FIG. 2D. A protection film 290 is conformallydepositing over the structure of FIG. 2C. The protection film 290 mayinclude suitable dielectric materials, such as silicon oxide, siliconnitride, silicon oxynitride, or the like. In some embodiments, the oxideof the protection film 290 may be undoped. The deposition process mayinclude CVD or the like. In some embodiments, a material of theprotection film 290 is chosen such that a refractive index of theprotection film 290 is similar to that of the underlying layer (e.g.,the portion P12 of the ILD layer ILD1 in the present embodiments), suchthat light may enter the underlying layer (e.g., the portion P12 of theILD layer ILD1) without interface reflection. For example, a differencebetween the refractive index of the protection film 290 and therefractive index of the ILD layer ILD1 is less than about 0.1. In someembodiments, the protection film 290 and the underlying layer (e.g., ILDlayer ILD1) may include the same material, such as silicon oxide. Insome embodiments, the protection film 290 and the underlying layer(e.g., ILD layer ILD1) may include suitable low-k materials. In someother embodiments, the protection film 290 and the underlying layer(e.g., ILD layer ILD1) may include different materials.

Through the deposition process, the protection film 290 may has portions292 on the sidewalls of the opening O2, a portion 294 on a bottom of theopening O2, and a portion 296 out of the opening O2. For example, insome embodiments the portion 292 is in contact with the sidewalls of theILD1-ILD9, the etch stop layer ESL, and the oxide layer IL. In someembodiments, the portion 294 is in contact with the exposed top surfaceof the portion P12 of the ILD layer ILD1. In some embodiments, theportion 296 of the protection film 290 is over a top surface andsidewalls of the patterned mask PM1.

Reference is made to FIG. 2E. The patterned mask PM1 (referring to FIG.2D) is removed by suitable ashing process, such that the portion 296 ofthe protection film 290 (referring to FIG. 2D) is also removed. Throughthe configuration, the portions 292 and 294 of the protection film 290remains and serve as a protection layer 290′. The protection layer 290′may passivate the sidewalls of the opening O2 and the bottom of theopening O2.

In some cases, due to the etch selectivity among the the etch stoplayers ESL, the oxide layers OL, and the ILD layers ILD1-ILD9, theetching process for forming the opening O2 may result in weak points(e.g., peeling and/or small gaps) at the sidewalls of the opening O2 atthe interface between adjacent two of the etch stop layers ESL, theoxide layers OL, and the ILD layers ILD1-ILD9. In absence of theprotection layer 290′, moisture may penetrate the ILD layers ILD1-ILDand the oxide layers OL from these weak points, and therefore damagesthe metal layers M1-M6 and the metal vias V1-V5 in the metal-dielectricstack 270.

In the present embodiments, the protection layer 290′ passivates theexposed sidewalls of the etch stop layers ESL, the oxide layers OL, andthe ILD layers ILD1-ILD9, thereby protecting the weak points from beingexposed to moisture in air. Through the configuration, moisture may notpenetrate the ILD layers ILD1-ILD and the oxide layers OL from the weakpoints, thereby protecting the metal layers M1-M6 and the metal viasV1-V5 from moisture.

FIGS. 3A-3B illustrate a method for fabricating a photonic device (e.g.,the photonic device 100 in FIG. 1) at various intermediate stages ofmanufacture according to various embodiments of the present disclosure.The present embodiments are similar to those illustrated in theembodiments of FIG. 2A-2E, except the profile of the opening O2 and theprotection layer 290′.

Reference is made to FIG. 3A. One or more etching processes areperformed to remove portions of the ILD layers ILD1-ILD9, the etch stoplayers ESL, and the oxide layers OL through the opening PMO1 of thepatterned mask PM1, thereby forming an opening O2 vertically overlappingthe coupler structure 416C. The etching process may be performed suchthat a top surface of the ILD layer ILD1 is exposed. In the presentembodiments, since the etch stop layer ESL may have a higher etchresistance to the etching process than the oxide layers OL and the ILDlayers ILD1-ILD9 during the formation of the opening O2, the sidewallsof the ILD layers ILD1-ILD9 and the oxide layers OL may be recessed morethan the sidewalls of the etch stop layers ESL. For example, thesidewalls of the ILD layers ILD1-ILD9 and the oxide layers OL arerecessed and concave. Furthermore, in some embodiments, during theformation of the opening O2, an etch rate at edge may be greater thanthe etch rate at center, such that the formed opening O2 may have aconvex bottom. For example, the portion P12 of the ILD layer ILD1 has aconvex top surface exposed by the opening O2 herein. The formation ofthe opening O2 may be similar to the process illustrated in theembodiments of FIG. 2C, and therefore not repeated herein.

Reference is made to FIG. 3B. A protection layer 290′ is formed onsidewalls and the bottom of the opening O2. The protection layer 290′may have a conformal profile as that of the sidewalls and the bottom ofthe opening O2. For example, the portion 292 of the protection layer290′ may have recesses according to the recesses on sidewalls of theopening O2 (e.g., the exposed sidewalls of the ILD layers ILD1-ILD9, theetch stop layers ESL, and the oxide layers), and the portion 294 of theprotection layer 290′ may have a convex top surface according to thebottom of the opening O2 (e.g., the convex top surface of the portionP12 of the ILD layer ILD1). The formation of the protection layer 290′may be similar to the process illustrated in the embodiments of FIGS.2D-2E, and therefore not repeated herein.

FIGS. 4A-4D illustrate a method for fabricating a photonic device (e.g.,the photonic device 100 in FIG. 1) at various intermediate stages ofmanufacture according to various embodiments of the present disclosure.The present embodiments are similar to those illustrated in theembodiments of FIG. 2A-2E, except the formation process of theprotection layer 290′.

Reference is made to FIG. 4A. After the formation of the opening O2 asshown in FIG. 2C, a protection filling material 390 is deposited overthe patterned mask PM1, thereby filling the opening O2 and the openingPMO1 of the patterned mask PM1. The protection filling material 390 mayinclude suitable dielectric materials, such as silicon oxide, siliconnitride, silicon oxynitride, or the like. The deposition process mayinclude CVD or the like. In some embodiments, a material of theprotection filling material 390 is chosen such that a refractive indexof the protection filling material 390 is similar to that of theunderlying layer (e.g., ILD layer ILD1 in the present embodiments). Forexample, a difference between the refractive index of the protectionfilling material 390 and the refractive index of the ILD layer ILD1 isless than about 0.1. In some embodiments, the protection fillingmaterial 390 and the underlying layer (e.g., the portion P12 of ILDlayer ILD1 in the present embodiments) may include the same material,such as silicon oxide. In some embodiments, the protection fillingmaterial 390 and the underlying layer (e.g., the portion P12 of ILDlayer ILD1 in the present embodiments) may include suitable low-kmaterials. In some other embodiments, the protection filling material390 and the underlying layer (e.g., the portion P12 of ILD layer ILD1)may include different materials.

Reference is made to FIG. 4B. A patterned mask PM2 is formed over theprotection filling material 390. The patterned mask PM2 has an openingPMO2 aligning with respect to the opening O2. The patterned mask PM2 mayinclude suitable organic material, such as photoresist. For example, aphotoresist is coated over the protection filling material 390 and thenpatterned using photolithography techniques to have the opening PMO2exposing portions of the protection filling material 390, therebyforming the patterned mask PM2.

Reference is made to FIG. 4C. One or more etching processes areperformed to remove portions of the protection filling material 390(referring to FIG. 4B) through the opening PMO2 of the patterned maskPM2, thereby forming a protection hole 3900 in the protection fillingmaterial 390 (referring to FIG. 4B). Parameters of the etching processesare controlled such that a remaining portion of the protection fillingmaterial 390 (referring to FIG. 4B) forms a protection layer 390′. Insome embodiments, the protection layer 390′ includes a portion 392covering the sidewalls of the opening O2, a portion 394 covering thebottom of the opening O2, and a portion 396 out of the opening O2. Forexample, the portion 396 of the protection layer 390′ is over a topsurface and sidewalls of the patterned mask PM1.

Reference is made to FIG. 4D. After the etching processes, the patternedmasks PM1 and PM2 are removed by suitable ashing processes, such thatthe portion 396 of the protection layer 390′ (referring to FIG. 4C) outof the opening O2 is also removed. Through the configuration, theportions 392 and 394 of the protection layer 390′ remains (referring toFIG. 4C) and serve as a protection layer 390″. The protection layer 390″may passivate the sidewalls of the opening O2 and the bottom of theopening O2.

FIG. 5 is a cross-sectional view of a photonic device according to someembodiments of the present disclosure. The present embodiments aresimilar to those illustrated in the embodiments of FIG. 4A-4D, exceptthe profile of the opening O2 and the protection layer 390″. In thepresent embodiments, since the etch stop layer ESL may have a higheretch resistance to the etching process than other ILD layers ILD1-ILD9and oxide layers OL during the formation of the opening O2, thesidewalls of the formed opening O2 may have recesses. Furthermore, insome embodiments, during the formation of opening O2, the etch rate atedge may be greater than the etch rate at center, such that the formedopening O2 may have a convex bottom. For example, the portion P12 of theILD layer ILD1 has a convex top surface exposed by the opening O2herein.

In the present embodiments, the protection layer 390″ is non-conformallyformed on sidewalls and the bottom of the opening O2, such that he innersurfaces of the protection layer 390″ may have a profile different fromthat of the sidewalls and the bottom of the opening O2. For example, inthe present embodiments, the portion 392 of the protection layer 390″have substantially flat inner sidewalls, and the portion 394 of theprotection layer 390″ have a substantially planar top surface. Theformation of the protection layer 390″ may be similar to the processillustrated in the embodiments of FIGS. 4A-4D, and therefore notrepeated herein.

FIG. 6 is a cross-sectional view of a photonic device according to someembodiments of the present disclosure. The present embodiments aresimilar to those illustrated in the embodiments of FIGS. 2A-2E or theembodiments of FIGS. 4A-4D, except the depth of the opening O2. In thepresent embodiments, the etching process may be controlled such that theexposed portion P12 of the ILD layer ILD1 may not be recessed. Forexample, the exposed portion P12 of the ILD layer ILD1 may havesubstantially the same thickness as that of other portions P11 of theILD layer ILD1. Through the configuration, a light source or a fiber maybe optically coupled to the coupler structure 416C through the portion292 of the protection layer 290′, the unrecessed portion P12 of the ILDlayer ILD1, the underlying etch stop layer ESL, the ILD layer ILD0, thelayers 250, 260, and the dielectric layer DL. In the presentembodiments, the protection layer 290′ may be formed by the processshown in the embodiments of FIGS. 2A-2E. In some other embodiments, theprotection layer 290′ may be formed by the process shown in theembodiments of FIGS. 4A-4D and therefore referred to as the protectionlayer 390″. Other details of the present embodiments are similar tothose aforementioned, and therefore not repeated herein.

FIG. 7 is a cross-sectional view of a photonic device according to someembodiments of the present disclosure. The present embodiments aresimilar to those illustrated in the embodiments of FIG. 2A-2E or theembodiments of FIG. 4A-4D, except the depth of the opening O2. In thepresent embodiments, the opening O2 extends to the ILD layer ILD0, andthe formed protection layer 290′ may be in contact with a top surface ofthe ILD layer ILD0. In the present embodiments, the etching process maybe controlled such that the opening O2 exposes a portion P02 of the ILDlayer ILD0, and the exposed portion P02 of the ILD layer ILD0 isrecessed and therefore thinner than other portions P01 of the ILD layerILD0. Through the configuration, a light source or a fiber may beoptically coupled to the coupler structure 416C through the portion 292of the protection layer 290′, the recessed portion P02 of the ILD layerILD0, the layers 250, 260, and the dielectric layer DL.

In some embodiments, a material of the protection layer 290′ is chosensuch that a refractive index of the protection layer 290′ is similar tothat of the underlying layer (e.g., the portion P02 of the ILD layerILD0 in the present embodiments), such that light may enter theunderlying layer (e.g., the portion P02 of the ILD layer ILD0) withoutinterface reflection. For example, a difference between the refractiveindex of the protection layer 290″ and the refractive index of the ILDlayer ILD0 is less than about 0.1. In some embodiments, the protectionlayer 290′ and the underlying layer (e.g., ILD layer ILD0) may includethe same material, such as silicon oxide. In some other embodiments, theprotection layer 290′ and the underlying layer (e.g., ILD layer ILD0)may include different materials. In the present embodiments, theprotection layer 290′ may be formed by the process shown in theembodiments of FIGS. 2A-2E. In some other embodiments, the protectionlayer 290′ may be formed by the process shown in the embodiments ofFIGS. 4A-4D and therefore referred to as the protection layer 390″.Other details of the present embodiments are similar to thoseaforementioned, and therefore not repeated herein.

FIG. 8 is a cross-sectional view of a photonic device according to someembodiments of the present disclosure. The present embodiments issimilar to those illustrated in the embodiments of FIG. 7, except thedepth of the opening O2. In the present embodiments, the etching processmay be controlled such that the exposed portion P02 of the ILD layerILD0 is not recessed. For example, the exposed portion P02 of the ILDlayer ILD0 may have a thickness substantially the same as that of otherportions P01 of the ILD layer ILD0. Through the configuration, a lightsource or a fiber may be optically coupled to the coupler structure 416Cthrough the portion 292 of the protection layer 290′, the unrecessedportion P02 of the ILD layer ILD0, the layers 250, 260, and thedielectric layer DL. Other details of the present embodiments aresimilar to the embodiments of FIG. 7, and therefore not repeated herein.

Based on the above discussions, it can be seen that the presentdisclosure offers advantages to the photonic device. It is understood,however, that other embodiments may offer additional advantages, and notall advantages are necessarily disclosed herein, and that no particularadvantage is required for all embodiments. One advantage is that aprotection layer is formed in the optical coupler opening forpassivating sidewalls of etch stop layer and ILD layers, such thatmoisture may not penetrate the ILD layers from weak points, therebyprotecting the metallization pattern from moisture. Another advantage isthat a material of the protection layer is chosen to reduce interfacereflection between the protection layer and the underlying layer,thereby improving the coupling efficiency.

According to some embodiments of the present disclosure, a method forfabricating a photonic device is provided. The method includes formingan optical coupler and a waveguide structure connected to the opticalcoupler over a semiconductor substrate; forming a metal-dielectric stackover the optical coupler and the waveguide structure; etching a hole inthe metal-dielectric stack and vertically overlapping the opticalcoupler; and forming a protection layer on a sidewall and a bottom ofthe hole.

According to some embodiments of the present disclosure, a method forfabricating a photonic device is provided. The method includes formingan optical coupler and a waveguide structure connected to the opticalcoupler over a semiconductor substrate; forming a first dielectric layerover the optical coupler and the waveguide structure; forming a etchstop layer over the first dielectric layer; forming a second dielectriclayer over the etch stop layer; etching a hole in at least the etch stoplayer and the second dielectric layer above the optical coupler, suchthat a sidewall of the etch stop layer and a sidewall of the seconddielectric layer are exposed by the hole; and forming a protection layeron the exposed sidewall of the etch stop layer and the exposed sidewallof the second dielectric layer.

According to some embodiments of the present disclosure, a photonicdevice includes an optical coupler, a waveguide structure, ametal-dielectric stack, and a protection layer. The waveguide structureis connected to the optical coupler. The metal-dielectric stack is overthe optical coupler and the waveguide structure, in which themetal-dielectric stack has a hole above the optical coupler. Theprotection layer has a first portion over a sidewall of the hole.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for fabricating a photonic device,comprising: forming an optical coupler and a waveguide structureconnected to the optical coupler over a semiconductor substrate; forminga metal-dielectric stack over the optical coupler and the waveguidestructure; etching a hole in the metal-dielectric stack and verticallyoverlapping the optical coupler; and forming a protection layer on asidewall and a bottom of the hole.
 2. The method of claim 1, whereinetching the hole is performed such that a top surface of a dielectriclayer of the metal-dielectric stack is exposed by the hole, and formingthe protection layer is performed such that the protection layer is incontact with the top surface of the dielectric layer.
 3. The method ofclaim 2, where forming the protection layer is performed such that theprotection layer has the same material as that of the dielectric layer.4. The method of claim 2, wherein forming the protection layer isperformed such that a difference between a refractive index of theprotection layer and a refractive index of the dielectric layer is lessthan about 0.1.
 5. The method of claim 1, wherein the protection layeris made of a low-k material.
 6. The method of claim 1, furthercomprising: forming a patterned mask over the metal-dielectric stackprior to etching the hole in the metal-dielectric stack, wherein etchingthe hole is performed with the patterned mask in place.
 7. The method ofclaim 6, wherein forming the protection layer comprises: depositing aprotection film over the patterned mask after etching the hole; andremoving a portion of the protection film out of the hole.
 8. The methodof claim 6, wherein forming the protection layer comprises: depositing aprotection material over the patterned mask to fill the hole in themetal-dielectric stack after etching the hole; etching a protection holein the protection material above the optical coupler; and removing aportion of the protection material out of the hole in themetal-dielectric stack.
 9. The method of claim 1, further comprising:forming a photodetector over the semiconductor substrate prior theforming the metal-dielectric stack, wherein forming the metal-dielectricstack is performed such that the metal-dielectric stack comprises ametallization pattern connected to the photodetector.
 10. A method forfabricating a photonic device, comprising: forming an optical couplerand a waveguide structure connected to the optical coupler over asemiconductor substrate; forming a first dielectric layer over theoptical coupler and the waveguide structure; forming an etch stop layerover the first dielectric layer; forming a second dielectric layer overthe etch stop layer; etching a hole in at least the etch stop layer andthe second dielectric layer above the optical coupler, such that asidewall of the etch stop layer and a sidewall of the second dielectriclayer are exposed by the hole; and forming a protection layer on theexposed sidewall of the etch stop layer and the exposed sidewall of thesecond dielectric layer.
 11. The method of claim 10, wherein forming theprotection layer is performed such that the protection layer isconformal to the exposed sidewall of the etch stop layer and the exposedsidewall of the second dielectric layer.
 12. The method of claim 10,wherein etching the hole is performed such that the exposed sidewall ofthe second dielectric layer is recessed more than the exposed sidewallof the etch stop layer.
 13. The method of claim 10, wherein forming theprotection layer is performed such that the protection layer is incontact with a top surface of the first dielectric layer.
 14. The methodof claim 13, further comprising: forming a photodetector over thesemiconductor substrate prior the forming the first dielectric layer,wherein forming the first dielectric layer is performed such that thefirst dielectric layer comprises a conductive contact connected to thephotodetector.
 15. The method of claim 13, further comprising: forming aphotodetector over the semiconductor substrate prior the forming thefirst dielectric layer, wherein forming the first dielectric layer isperformed such that the first dielectric layer comprises a metal layerelectrically connected to the photodetector.
 16. A photonic device,comprising: an optical coupler; a waveguide structure connected to theoptical coupler; a metal-dielectric stack over the optical coupler andthe waveguide structure, wherein the metal-dielectric stack has a holeabove the optical coupler; and a protection layer having a first portionover a sidewall of the hole.
 17. The photonic device of claim 16,wherein the metal-dielectric stack has a first dielectric layer, asecond dielectric layer, and an etch stop layer between the firstdielectric layer and the second dielectric layer, wherein the protectionlayer is in contact with a sidewall of the first dielectric layer, asidewall of the second dielectric layer, and a sidewall of the etch stoplayer.
 18. The photonic device of claim 16, wherein the protection layerfurther has a second portion over a bottom of the hole.
 19. The photonicdevice of claim 18, wherein the metal-dielectric stack has a dielectriclayer in contact with the second portion of the protection layer, and adifference between a refractive index of the protection layer and arefractive index of the dielectric layer is less than about 0.1.
 20. Thephotonic device of claim 18, wherein the second portion of theprotection layer has a convex top surface in the hole in themetal-dielectric stack.